/Engine/Source/Runtime/GeometryCore/Public/DynamicMesh/MeshTangents.h
Set tangent and bitangent at a vertex of triangle for per-triangle computed tangents.
void SetPerTriangleTangent ( int TriangleID, int TriVertIdx, const [TVector](API\Runtime\Core\Math\TVector)< RealType > & Tangent, const [TVector](API\Runtime\Core\Math\TVector)< RealType > & Bitangent )